1. Field of the Invention
The present invention is directed to diagnostic x-ray systems which produce a diagnostic x-ray image, and is specifically directed to systems of this type having an adjustable primary radiation diaphragm.
2. Description of the Prior Art
Radiation systems, for example computer tomography systems, are known in the art wherein an x-ray fan beam is generated for diagnostic purposes, the fan beam being formed (gated) by an adjustable primary radiation diaphragm. In known computer tomography systems of this type the primary radiation diaphragm is fashioned as a slit diaphragm, which defines the shape of the x-ray fan beam. The fan beam, in turn, defines the dose profile in the patient, and thus the thickness of the slice in an exposure. The fan beam thus also influences the dose load on the patient and the intensity of the detector signal from which the image data are acquired. For setting various slice thicknesses, it is necessary to set various apertures of the primary radiation diaphragm. In order to achieve an optimally high quantum yield at the radiation detector, it is necessary to insure that the center of area of the radiation fan beam be centrally incident on the detector. This means that the focus of the x-ray radiator, the center line of the primary radiation diaphragm, and the center line of the radiation detector should coincide for an optimum irradiation of the detector. Moreover, in order to insure a low dose load on the patient, it is necessary to minimize the number of required exposures. It is helpful for this purpose if the quality of each individual exposure, and thus its diagnostic content, is optimally high.
In general, the beam geometry is modified by the dynamic influences caused by rotation of the rotating part of the computer tomography apparatus and/or by thermal influences, particularly in the x-ray radiator. Such modification of the beam geometry, if not corrected, can result in a degradation of the image.